API 651 - 6 (Methods of Cathodic Protection for Corrosion Control)

Question 1

there are two methods of cathodic protection for corrosion control:

Answer 1

galvanic and impressed current

Question 2

a galvanic cathodic protection system uses a metal more _____ than the structure to be protected to supply the current required to stop corrosion.

Answer 2

noble

Question 3

Metals commonly used as sacrificial anodes in soil are:

Answer 3

magnesium and zinc

Question 4

galvanic systems are normally applied only to:

Answer 4

small diameter tanks

Question 5

No external power supply is required, installation is relatively easy, capital investment is low for small diameter tanks, maintenance costs are minimal, stray current problems are rare, and less monitoring is required. These are all advantages of:

Answer 5

a galvanic system

Question 6

Driving potential is limited, current output is low,the method is limited to use in low resistivity soils , and the method is not practical for protection of large bare structures.These are all disadvantages of:

Answer 6

a galvanic system

Question 7

impressed current systems of cathodic protection use:

Answer 7

direct current

Question 8

In an impressed current system,direct current is used. This current is provided by:

Answer 8

a rectifier attached to an AC power source

Question 9

A typical cathodic protection rectifier has two major components :

Answer 9

A step-down transformer to reduce AC supply voltage & rectifying elements to produce DC output.

Question 10

A cathodic protection rectifier unit may be obtained with either

Answer 10

selenium or silicon rectifier elements

Question 11

Impressed current anodes are made of materials such as:

Answer 11

graphite,steel,high silicon cast iron,or mixed metal oxides on titanium

Question 12

Impressed current anodes are usually buried in a _________ to extend their life and reduce circuit resistance.

Answer 12

coke breeze back-fill